Regulatory Matters (Details) $ in Millions	1 Months Ended	12 Months Ended
	May 31, 2010 orders	Dec. 31, 2016 USD ($)	Jun. 30, 2015 MW	Dec. 20, 2013 USD ($)	Jul. 05, 2012 USD ($) owners	Dec. 31, 2011 USD ($)
Regulatory Assets [Line Items]
Out-of-market subsidy payments		$ 7,600
Out of Market Subsidy Payment term		12 years
Number of significant orders issued by FERC | orders	2
SECA charges owed by BP Energy						$ 22
Regulatory Charges Settled by Third Party					$ 24
Number of PJM Transmission Owners Who Filed Motion | owners					3
Regulatory Charges Settled by Third Party, Additional					$ 1
Genon [Member]
Regulatory Assets [Line Items]
Regulatory payments sought				$ 22
Carlsbad Energy Center [Member]
Regulatory Assets [Line Items]
Power Generation Capacity, Megawatts | MW			500